PROJECT SUMMARY/ABSTRACT In this application the researchers propose to 1) characterize ?serosal bridges? (SBs), a previously unknown internal route that facilitates antigen and cell transport between the female reproductive tract (FRT) and the gastro-intestinal (GI) tract; and 2) assess the essentiality of SBs and cell migration for transport of Chlamydia spp. from the FRT to the GI tract. The team showed that vaginal immunization with ovalbumin-conjugated 20 nm nanoparticles (NPs) induces serum IgG and primes the intestinal mucosa for secretion of IgA. Surprisingly, it was found that vaginally-instilled soluble antigens and NPs are ?delivered? to the lower stomach and duodenum. Moreover, vaginally-instilled Chlamydia spp. elementary bodies (300-450 nm) reach SBs and intestinal serosa within 1-3 hours. In humans and animals Chlamydia spp. spreads from the FRT and persists in the GI tract, where it is resistant to azithromycin treatment. In mice, Chlamydia disseminates internally however, how it transits from the FRT to the GI tract remains unknown. Completion of the proposed work will be critical for understanding dissemination of Chlamydia from the FRT to the GI tract, as well as for developing vaccination strategies to target this pathogen.